You can use sed command
$ cat os.txt
BEST
UNIX
Unix
uNiX
Sed supports "i" or "I" for "case insensitive" search and replacement
$ sed 's/unix/BEST/i' os.txt
BEST
BEST
BEST
BEST
If you need to use vi try this command
1,$ s/apple/orange/gI
Question
Basically I want to do the following replacement using vi:
Apple->Orange
apple->orange
APPLE->ORANGE
Is there any way to do it in one line?
Solution
You can use sed command
$ cat os.txt
BEST
UNIX
Unix
uNiX
Sed supports "i" or "I" for "case insensitive" search and replacement
$ sed 's/unix/BEST/i' os.txt
BEST
BEST
BEST
BEST
If you need to use vi try this command
1,$ s/apple/orange/gI